Camshaft phasers for varying the timing of combustion valves in an internal combustion engine transmit crankshaft torque to the engine camshaft, allowing varied timing of the camshaft relative to the crankshaft position.
It is known in some prior art phaser applications to employ one or more toroidal (also referred to herein as “helical”) torsional bias springs within a phaser, grounded at opposite ends to the stator and rotor, respectively, to counterbalance a portion of the friction torque of the camshaft due to the valve train components (lifters, cam journals, cam driven accessories, etc.).
Such a bias spring is especially useful in exhaust phasing applications because the friction torque from the exhaust camshaft acts to retard the camshaft in opposition to the timing advance default position. The bias spring helps the exhaust phaser to return to its default (locked) position on engine shutdown and allows more balanced control of the phaser at intermediate positions.
Intake phasers also may include a bias spring having a somewhat lower spring constant to provide more balanced advancing and retarding rates while not preventing the phaser from reaching the retard default position.
In some prior art phasers, it is known to utilize a flat, spiral wound spring having a squared inner end, similar to the long-standing application of such springs in watches and clocks. In these applications, the squared inner end is grounded by being wrapped around a square sided mandrel. A shortcoming of this design is that, when a torsional force is applied to the spring, the squared inner end spreads open as the flats of the square ramp up the mating flat surfaces of the mandrel.
More typically however, prior art cam phaser bias springs are helically wound, utilizing spring ends (tangs) that are bent either radially outward or axially and engage a slot to ground the spring to the phaser component. A shortcoming of such prior art phasers using helical bias springs is that the shape required in the rotor and/or stator to anchor and restrain a radial or axial tang is known to cause difficulties in forming powdered metal components.
In addition, an axially bent end increases the axial length of the phaser, which is undesirable.
Further, in pulley phaser applications wherein the phaser must be sealed to prevent oil leakage to the exterior of the part, packaging is difficult because a cover plug is required for plugging the access hole for the central cam bolt. The space required for the cover plug consumes the space otherwise usable for an axial or radial spring end.
Still further, a radially-outward spring end requires adding seal plates or significant increases in radial packaging volume of the entire phaser.
What is needed in the art is an improved bias system for a camshaft phaser wherein a helical bias spring is mechanically anchored to the rotor end without resort to an axial or radial tang.
It is a principal object of the present invention to reduce the size, complexity, and manufacturing cost of a camshaft phaser.